Light-emitting device

ABSTRACT

The present disclosure provides a light-emitting device. The light-emitting device comprises: a substrate; an intermediate layer on the substrate; a first window layer comprising a first semiconductor optical layer on the intermediate layer and a second semiconductor optical layer on the first semiconductor optical layer; and a light-emitting stack on the second semiconductor optical layer; wherein a difference between the lattice constant of the intermediate layer and the lattice constant of the first semiconductor optical layer is greater than 2.3 Å.

RELATED APPLICATION

This application is a continuation application of a previously filedU.S. patent application Ser. No. 14/992,785 filed on Jan. 11, 2016,entitled as “LIGHT-EMITTING DEVICE”, which is a continuation applicationof a previously filed U.S. patent application Ser. No. 14/038,969 filedon Sep. 27, 2013, entitled as “LIGHT-EMITTING DEVICE WITH INTERMEDIATELAYER”, which is a continuation-in-part of a previously filed U.S.patent application Ser. No. 13/050,444 filed on Mar. 17, 2011, entitledas “LIGHT-EMITTING DEVICE”. The disclosures of all references citedherein are incorporated by reference.

BACKGROUND

1. Technical Field

The present disclosure relates to a method for making a light-emittingdevice, and in particular to a method for making a light-emitting devicecomprising a bonding layer.

2. Description of the Related Art

The light-emitting diodes (LEDs) of the solid-state lighting elementshave the characteristics of the low power consumption, low heatgeneration, long operational life, shockproof, small volume, quickresponse and good opto-electrical property like light emission with astable wavelength, so the LEDs have been widely used in householdappliances, indicator light of instruments, and opto-electricalproducts, etc.

Recently, a light-emitting device with a flip-chip package structurehaving light emitted toward the substrate is developed. However, how toimprove the light-emitting efficiency of the light-emitting device isstill an important issue in this art.

SUMMARY OF THE DISCLOSURE

The present disclosure provides a light-emitting device. Thelight-emitting device comprises: a substrate; an intermediate layer onthe substrate; a first window layer comprising a first semiconductoroptical layer on the intermediate layer and a second semiconductoroptical layer on the first semiconductor optical layer; and alight-emitting stack on the second semiconductor optical layer; whereina difference between the lattice constant of the intermediate layer andthe lattice constant of the first semiconductor optical layer is greaterthan 2.3 Å.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide easy understanding ofthe application, and are incorporated herein and constitute a part ofthis specification. The drawings illustrate the embodiments of theapplication and, together with the description, serve to illustrate theprinciples of the application.

FIG. 1 shows a cross-sectional view of a light-emitting device inaccordance with the first embodiment of the present disclosure.

FIGS. 2A to 2D show a cross-sectional view of a light-emitting device inaccordance with the second embodiment of the present disclosure.

FIG. 3 shows a cross-sectional view of a light-emitting device inaccordance with the third embodiment of the present disclosure.

FIG. 4 shows a cross-sectional view of a light-emitting device inaccordance with the fourth embodiment of the present disclosure.

FIG. 5 shows a cross-sectional view of a light-emitting device inaccordance with the fifth embodiment of the present disclosure.

FIG. 6 shows a cross-sectional view of a light-emitting device inaccordance with the sixth embodiment of the present disclosure.

FIGS. 7A to 7F are cross-sectional views showing a method of making thelight-emitting device in accordance with the first embodiment of thepresent disclosure.

FIGS. 8A to 8B show cross-sectional views of a light-emitting device inaccordance with the seventh and the eighth embodiments of the presentdisclosure.

FIGS. 9A to 9G show a method of making a light-emitting device inaccordance with the seventh and the eighth embodiments of the presentdisclosure.

DETAILED DESCRIPTION OF THE EMBODIMENTS

To better and concisely explain the disclosure, the same name or thesame reference number given or appeared in different paragraphs orfigures along the specification should has the same or equivalentmeanings while it is once defined anywhere of the disclosure.

The following shows the description of the embodiments of the presentdisclosure in accordance with the drawings.

FIG. 1 discloses a light-emitting device 100 according to the firstembodiment of the present disclosure. The light-emitting device 100comprises a permanent substrate 10, an intermediate layer 11 formed onthe permanent substrate 10, a transparent bonding layer 15, a firstsemiconductor window layer 13 bonded to the intermediate layer 11through the transparent bonding layer 15, a light-emitting stack 12formed on the first semiconductor window layer 13, a secondsemiconductor window layer 14 formed on the light-emitting stack 12opposite to the first semiconductor window layer 13. In this embodiment,the intermediate layer 11 has a refractive index between the refractiveindex of the permanent substrate 10 and the refractive index of thefirst semiconductor window layer 13. For example, the permanentsubstrate 10 is a sapphire substrate having the refractive index of 1.7,the intermediate layer 11 comprises gallium nitride or diamond havingthe refractive index of 2.4, and the first semiconductor window layer 13is gallium phosphide (GaP) having the refractive index of 3.37. Sincethe refractive index is gradually reduced from the first semiconductorwindow layer 13 to the permanent substrate 10, the total lightreflection in the light-emitting device 100 can be attenuated. In oneembodiment, the permanent substrate 10 has the refractive index rangingfrom 2.4 to 3.4, the intermediate layer 11 has the refractive indexranging from 1.7 to 3.4, and the first semiconductor window layer 13 hasthe refractive index ranging from 1.4 to 1.7. In addition, the permanentsubstrate 10 is a patterned substrate for improving light efficiency ofthe light-emitting stack 12. Alternatively, the permanent substrate 10can have a flat surface. In one embodiment, when the permanent substrate10 has a flat surface, the intermediate layer 11 can comprises aplurality of pores formed therein so as to form a porous structure (notshown) for scattering light. The pores are formed by dry etching such asinductive coupling plasma (ICP), or wet etching using potassiumhydroxide, oxalic acid, sulfuric-acid, phosphoric acid or combinationsthereof.

Referring to FIG. 1, the first semiconductor window layer 13 comprises arecess portion 131 and a flat surface 132. The light-emitting stack 12is formed on the flat surface 132. The light-emitting device 100 furthercomprises a plurality of patterned contacts 171 formed on the secondsemiconductor window layer 14 for spreading current. In addition, thelight-emitting device 100 further comprises a mirror layer 18. In thisembodiment, the mirror layer 18 comprises an insulation layer 181 forpreventing undesired current path, and a reflective layer 182 formed onportions of the insulation layer 181 for reflecting the light toward thefirst semiconductor window layer 13. The insulation layer 181 covers aside surface and the recess portion 131 of the first semiconductorwindow layer 13, and further covers side walls of the light-emittingstack 12 and the second semiconductor window layer 14. Moreover, theinsulation layer 181 is also formed on the second semiconductor windowlayer 14, but not formed on the contacts 171. The light-emitting device100 further comprises a first electrode 16 formed on the recess portion131 of the first semiconductor window layer 13, and a second electrode17 formed on the patterned contacts 171 and portions of the insulationlayer 181 for electrically connecting to the light-emitting stack 12 foremitting light. A gap 19 is formed between the reflective layer 182 andthe second electrode 17. The insulation layer 181 comprises oxide suchas SiO₂, Ta₂O₅, TiO₂, Al₂O₃, nitride such as Si₃N₄, AlN, or polymer. Thereflective layer 182 comprises metal, such as Al, Ag, Au or Cu.Alternatively, the insulation layer 181 and the reflective layer 182 cancomprise a multi-layer structure. Moreover, the mirror layer 18 canmerely comprise the insulation layer 181 having a multi-layer structure,such as distributed Bragg reflectors (DBR).

In this embodiment, the first semiconductor window layer 13 has a layerthickness greater than that of the second semiconductor window layer 14.The greater the thickness of the first semiconductor window layer 13,the easier the light escape from the light-emitting device 100 would be.In one embodiment, the first semiconductor window layer 13 has a layerthickness ranging from 1.2 μm to 10 μm. The second semiconductor windowlayer 14 has a layer thickness ranging from 0.1 μm to 5 μm.

In this embodiment, the light-emitting stack 12 comprises a p-typesemiconductor layer 121, an active layer 122, and an n-typesemiconductor layer 123. Each of the p-type semiconductor layer 121, theactive layer 122, and the n-type semiconductor layer 123 comprises groupIII-V compound semiconductor, such as GaN based material or GaP basedmaterial. The permanent substrate 10 is transparent and comprises glass,sapphire, or quartz. The transparent bonding layer 15 comprises indiumtin oxide (ITO), benzocyclobutene (BCB), epoxy resin (Epoxy),polydimethylsiloxane (PDMS), silicon oxide (SiO_(x)), aluminum oxide(Al₂O₃), titanium dioxide (TiO₂), silicon nitride (SiN_(x)), orcombinations thereof. The transparent bonding layer 15 can comprises amulti-layer structure and have a thickness ranging from 10 nm to 5 μm.

It is noted that the intermediate layer 11 can be bonded to the firstsemiconductor window layer 13 by a direct bonding without thetransparent bonding layer 15. The direct bonding is performed under atemperature of 200-500° C. and a pressure less than 1 mtorr, and acomposite material is formed at the interface between the intermediatelayer 11 and the first semiconductor window layer 13 during the directbonding process.

FIGS. 2A to 2D disclose a light-emitting device 200 according to thesecond embodiment of the present disclosure. The light-emitting device200 of the second embodiment has the similar structure with thelight-emitting device 100 of the first embodiment except that the mirrorlayer 18 further comprises a layer 183 formed on the secondsemiconductor window layer 14 and the contacts 171. The second electrode17 is formed on the layer 183. Since the contacts 171 ohmicly contactthe second semiconductor window layer 14, when a voltage is applied onthe second electrode 17, most current flows through the contacts 171 tothe second semiconductor window layer 14 for spreading current. Theinsulation layer 181 and the reflective layer 182 are merely formed onthe side wall of the light-emitting stack 12 and the first and secondsemiconductor window layers 13, 14. The contacts 171 contain metal suchas Cu, Al, In, Sn, Au, Pt, Zn, Ag, Ti, Ni, Pb, Pd, Ge, Ni, Cr, Cd, Co,Mn, Sb, Bi, Ga, Tl, Po, Ir, Re, Rh, Os, W, Li, Na, K, Be, Mg, Ca, Sr,Ba, Zr, Mo, La, Ge—Au, Be—Au, Cr—Au, Ag—Ti, Cu—Sn, Cu—Zn, Cu—Cd,Sn—Pb—Sb, Sn—Pb—Zn, Ni—Sn, Ni—Co, or Au alloy.

Referring to FIG. 2A, the layer 183 is made of metal comprising Au, Ni,Cu, Ag, or Al. Referring to FIGS. 2B to 2D, the layer 183 can be anomni-directional reflector (ODR) structure comprising a first layer 1831and a second layer 1832. Referring to FIG. 2B, the first layer 1831 isformed on the second semiconductor window layer 14 and the contacts 171,and the material of the first layer 1831 is ITO. The second layer 1832of Ag is formed on the ITO layer. Alternatively, the first layer 1831can be directly formed on the second window semiconductor layer 14without formation of the contacts 17 therebetween for ohmicly contactingwith the second window semiconductor layer 14. Referring to FIG. 2C, thefirst layer 1831 is formed on the second semiconductor window layer 14and portions of the contacts 171 wherein the material of the first layer1831 is SiO₂. The second layer 1832 comprising Ag, Al or Cu is formed onthe SiO₂ layer and the contacts 171 uncovered by the SiO₂ layer forelectrically connecting with second semiconductor window layer 14through the contacts 171. Referring to FIG. 2D, the first layer 1831 ofSiO₂ is formed on the second semiconductor window layer 14 and flushwith the contacts 171. The second layer 1832 is formed on the SiO₂layer.

FIG. 3 discloses a light-emitting device 300 according to the thirdembodiment of the present disclosure. The light-emitting device 300 ofthe third embodiment has the similar structure with the light-emittingdevice 100 of the first embodiment except that the first semiconductorwindow layer 13 has a scattering surface 134 facing toward the permanentsubstrate 10 for scattering the light emitted from the light-emittingstack 12. The permanent substrate 10 has a flat surface. The scatteringsurface 134 can be formed by surface texturing or doping. The surfacetexturing can be performed by etching.

FIG. 4 discloses a light-emitting device 400 according to the fourthembodiment of the present disclosure. The light-emitting device 400 ofthe fourth embodiment has the similar structure with the light-emittingdevice 100 of the first embodiment except that the light-emitting device400 further comprises a plurality of ohmic contact parts 161 formedbetween the transparent bonding layer 15 and the first semiconductorwindow layer 13 for uniformly spreading current. Moreover, the firstelectrode 16 has a finger electrode 162 extending through the firstsemiconductor window layer 13 for electrically connecting with one ofthe ohmic contact parts 161. In this embodiment, the ohmic contact parts161 are spaced apart from each other, and the transparent bonding layer15 comprises a transparent conductive layer 151 such as indium titaniumoxide (ITO) covering the ohmic contact parts 161 for electricalconnection therebetween. The transparent bonding layer 15 furthercomprises a transparent layer 152 comprising indium titanium oxide(ITO), silicon dioxide (SiO₂), or aluminum oxide (Al₂O₃). The ohmiccontact parts 161 comprises metal such as Ge, Au, Ni, Cu, orcombinations thereof.

FIG. 5 discloses a light-emitting device 500 according to the fifthembodiment of the present disclosure. The light-emitting device 500 ofthe fifth embodiment has the similar structure with the light-emittingdevice 100 of the first embodiment except that the insulation layer 181comprises a plurality of particles 1811 dispersed therein for providinga curved surface such that light refraction occurs at the curved surfaceto change a light-emitting angle. Each of the particles 1811 has adiameter ranging from 0.3 μm to 5 μm. The particles 1811 comprise glass,polymer, or ceramic material. The transparent bonding layer 15 can alsocomprises the particles for scattering light. The particles 1811 areformed within the insulation layer 181 by a spin-on process a printingprocess, or a dipping process.

FIG. 6 discloses a light-emitting device 600 according to the sixthembodiment of the present disclosure. The light-emitting device 600 ofthe sixth embodiment has the similar structure with the light-emittingdevice 400 of the first embodiment except that the first semiconductorwindow layer 13 has a smaller area than that of the transparent bondinglayer 15. Accordingly, there is no by-product formed on the firstsemiconductor window layer 13 which is produced from separating aplurality of the light-emitting diodes into an individual chip by laser,thereby improving light efficiency.

FIGS. 7A to 7G illustrate a method of making the light-emitting device100 according to the first embodiment of the present disclosure.Referring to FIG. 7A, the second semiconductor window layer 14 ofAlGaInP and the light-emitting stack 12 comprising the n-typesemiconductor layer 123, and the active layer 122, the p-typesemiconductor layer 121 are sequentially grown on a growth substrate 90.Subsequently, the first semiconductor window layer 13 of GaP is formedon the p-type semiconductor layer 121, and the transparent bonding layer15 comprising a bilayer structure of SiO₂ and Al₂O₃ is formed on thefirst semiconductor window layer 13. The growth substrate 90 comprisessapphire, silicon carbide, gallium nitride, gallium aluminum, andcombinations thereof.

Referring to FIG. 7B, the permanent substrate 10 is provided for growingthe intermediate layer 11 of GaN thereon. Before the growth of theintermediate layer 11, the permanent substrate 10 is etched to form apatterned substrate.

Referring to FIG. 7C, the intermediate layer 11 is bonded to the firstsemiconductor window layer 13 through the transparent bonding layer 15.

Referring to FIG. 7D, after removing the growth substrate 90, portionsof the n-type semiconductor layer 123, the active layer 122, the p-typesemiconductor layer 121, and the second semiconductor window layer 14are removed to expose the first semiconductor window layer 13.Furthermore, portions of the first semiconductor window layer 13 areremoved to form a recess portion 131 and a flat surface 132 on which thelight-emitting stack 12 and the second semiconductor window layer 14 areformed.

Referring to FIG. 7E, a plurality of patterned contacts 171 are formedon the second window semiconductor layer 14. Subsequently, theinsulation layer 181 is formed to cover side walls of the light-emittingstack 12 and the first semiconductor window layer 13, and further tocover the recess portion 131 of the first semiconductor window layer 13and the second semiconductor window layer 14, but not to cover thecontacts 171. The reflective layer 182 is formed on portions of theinsulation layer 181.

Referring to FIG. 7F, portions of the insulation layer 181 and thereflective layer 182 formed on the recess portion 131 of the firstsemiconductor window layer 13 are removed to expose parts of the firstsemiconductor window layer 13. The first electrode 16 is formed on theexposed first semiconductor window layer 13, and the second electrode 17is formed on the contacts 171 and portions of the insulation layer 180.

FIG. 8A discloses a light-emitting device 700 in accordance with theseventh embodiment of the present disclosure. The light-emitting device700 comprises a permanent substrate 10, an intermediate layer 11 on thepermanent substrate 10, a first window layer 112 on the intermediatelayer 11, and a light-emitting stack 12 on the first window layer 112.Besides, the light-emitting device 700 further comprises a second windowlayer 140 formed on the light-emitting stack 12 and is opposite to thefirst window layer 112 and comprises an insulation layer 181 covering asurface of the second window layer 140. A nucleation layer 110 isbetween the intermediate layer 11 and the first window layer 112 whichcomprises a first semiconductor optical layer 1120 and a secondsemiconductor optical layer 1122. The first window layer 112 inlight-emitting device 700 is configured to increase the light extractionin a lateral direction. The first semiconductor optical layer 1120 andthe second semiconductor optical layer 1122 are combined to extend thepath of the light within the light-emitting device 700 in order toincrease the light scattering in a lateral direction. The insulationlayer 181 comprises oxide such as SiO₂, Ta₂O₅, TiO₂, Al₂O₃, nitride suchas Si₃N₄, AlN, or polymer. Alternatively, the insulation layer 181 cancomprise a multi-layer structure. In another embodiment, the insulationlayer 181 can be a distributed Bragg reflector (DBR) layer to decreasethe amount of light passing through the side wall of the light-emittingstack 12. Moreover, the insulation layer 181 is configured as apassivation layer to protect the light-emitting stack 12 and the secondwindow layer 140 from reacting with gas surrounding the light-emittingdevice 700 during manufacturing process.

The first window layer 112 comprises a recess portion 131 and a flatsurface 132, wherein the flat surface 132 is connected to thelight-emitting stack 12 and the recess portion 131 is not covered by thelight-emitting stack 12. The insulation layer 181 covers a side surfaceand the recess portion 131 of the first window layer 112, and furthercovers side walls of the light-emitting stack 12 and the second windowlayer 140. The first window layer 112 further comprises a firstsemiconductor optical layer 1120 and a second semiconductor opticallayer 1122. Moreover, the insulation layer 181 is also formed on thesecond window layer 140, but not formed on the contacts 171. Thecontacts 171 are covered by an extension part 172 to form a secondelectrode 170. The light-emitting device 700 further comprises a firstelectrode 16 formed on the recess portion 131 of the first window layer112 not covered by the insulation layer 181, and the second electrode170 electrically connecting to the light-emitting stack 12 for emittinglight. The contacts 171 and the extension part 172 are configured toimprove current spreading. Moreover, the materials of contacts 171 andthe extension parts 172 are the same or different from other parts.

In this embodiment, the intermediate layer 11 comprises a nitridesemiconductor compound; the nucleation layer 110 and the firstsemiconductor optical layer 1120 comprise a phosphide semiconductorcompound. The nitride semiconductor compound can be gallium nitride(GaN), and the phosphide semiconductor compound can be gallium phosphide(GaP). The second semiconductor optical layer 1122 also comprises aphosphide semiconductor compound which is same as the material of thefirst semiconductor optical layer 1120. Then, the intermediate layer 11comprises gallium nitride (GaN) with a lattice constant of 3.1 Å and thefirst semiconductor optical layer 1120 comprises gallium phosphide (GaP)with a lattice constant of 5.45 Å. In other words, the intermediatelayer 11 and the first semiconductor optical layer 1120 comprisedifferent group III-V semiconductor compounds (i.e. GaN and GaP). Adifference between the lattice constant of the intermediate layer andthe lattice constant of the first semiconductor optical layer is greaterthan 1.5 Å. Preferably, the difference of lattice constants between theintermediate layer 11 and the first semiconductor optical layer 1120 islarger than 2.3 Å and having a lattice mismatch ratio of 74%. In orderto reduce the effect of the lattice mismatch, a nucleation layer 110having a thickness less than that of the first semiconductor opticallayer 1120 is formed in advance, wherein the nucleation layer 110 alsocomprises gallium phosphide (GaP). Then, the first semiconductor opticallayer 1120 is formed on a layer having a lattice constant matching withthe first semiconductor optical layer 1120. Moreover, the intermediatelayer 11 is also lattice mismatched with the permanent substrate 10,wherein the permanent substrate 10 is a non-semiconductor layer andcomprises sapphire.

In this embodiment, the intermediate layer 11 has a refractive indexbetween the refractive index of the permanent substrate 10 and therefractive index of the first window layer 112 or the nucleation layer110. For example, the permanent substrate 10 is a sapphire substratehaving the refractive index of 1.7, the intermediate layer 11 comprisesgallium nitride or diamond having the refractive index of 2.4, and thefirst window layer 112 with the nucleation layer 110 comprises galliumphosphide (GaP) having the refractive index of 3.37. In anotherembodiment, the permanent substrate 10 comprises a different materialand has the refractive index ranging from 1.4 to 1.7, the intermediatelayer 11 has the refractive index ranging from 1.7 to 3.4, and the firstwindow layer 112 along with the nucleation layer 110 has the refractiveindex ranging from 2.4 to 3.4. In another portion of the light-emittingdevice 700, the insulation layer 181 comprises silicon nitride (SiN) andhas a refractive index of 2.0 which is smaller than the refractive indexof the second window layer 140 which comprises aluminum gallium indiumphosphide and has a refractive index between 3.0˜3.5.

Since the refractive index is reduced from the first window layer 112 tothe permanent substrate 10, the total light reflection in thelight-emitting device 700 can be attenuated. Moreover, the refractiveindex is also reduced from the second window layer 140 (refractiveindex: 3.0˜3.5) to the air (refractive index: ˜1) through the insulationlayer 181 (refractive index: 2.0), and the total light reflection in thelight-emitting device 700 in another direction can be also attenuated.To sum up, the light-emitting device 700 comprises two groups of layershaving degraded refractive indexes in two directions wherein the twodirections are opposite to each other. Thus, the total internalreflections in two opposite directions within the light-emitting device700 are attenuated and the light emitting efficiency is improved.

In this embodiment, the permanent substrate 10 is a patterned substratefor improving light efficiency of the light-emitting stack 12.Alternatively, the permanent substrate 10 can have a flat surface forforming layers. In another embodiment, the intermediate layer 11 isformed on the flat surface of the permanent substrate 10 and comprises aplurality of pores for scattering light. The pores are formed by dryetching such as inductive coupling plasma (ICP), or wet etching usingpotassium hydroxide, oxalic acid, sulfuric-acid, phosphoric acid orcombinations thereof.

FIG. 8B discloses a light-emitting device 800 in accordance with theeighth embodiment of the present disclosure. The light-emitting device800 has a similar structure compared with the light-emitting device 700in FIG. 8A. Light-emitting device 800 further comprises a reflectivelayer 101 on the permanent substrate 10 and a carrier 103 formed on thereflective layer 101 through an adhesive layer 102. Thus, the reflectivelayer 101 is formed on a side of the substrate 10 opposing to a sideconnected to the light-emitting stack 12. In this embodiment, the lightemitted from the light-emitting stack 12 passing through the permanentsubstrate 10 is reflected by the reflective layer 101. The reflectedportion of the light passes the side wall 104 toward outside of thelight-emitting device 800, wherein the side wall 104 includes the sidesurfaces of the adhesive layer 102, the reflective layer 101, thepermanent substrate 10, the intermediate layer 11 and the first windowlayer 112. That is, the side wall 104 extends form the carrier 103 tothe recess portion 131 of the first window layer 112. Moreover, thecarrier attached to the reflective layer 101 is designed to have alarger width compared with the width of the light-emitting stack 12.Then, light is reflected by the reflective layer 101 and the amount ofthe light in a lateral direction is increased. The lateral directionbroadly represents a direction from the substrate 10 toward the ambientthrough the side wall 104, and the direction is not parallel to the sidewall 104.

FIGS. 9A-9G illustrate a method of making a light-emitting device inaccordance with the seventh and the eighth embodiment of the presentdisclosure. Referring to FIG. 9A, the second window layer 140 comprisingAlGaInP is formed on the growth substrate 90. The light-emitting stack12 comprising an n-type semiconductor layer 123, an active layer 122,and the p-type semiconductor layer 121 are sequentially formed on thesecond window layer 140. Then, the second semiconductor optical layer1122 is formed on the light-emitting stack 12 with a modified thicknessfor better epitaxy layer quality. The material of the growth substrate90 comprises sapphire, silicon carbide, gallium nitride, galliumaluminum, and combinations thereof. In another embodiment, thesemiconductor layer 121 can be an n-type semiconductor layer and thesemiconductor layer 123 can be a p-type semiconductor layer.

Referring to FIG. 9B, the intermediate layer 11, for example, a GaNlayer is formed on the permanent substrate 10. In this embodiment, thepermanent substrate 10 is a patterned substrate. Then, the nucleationlayer 110 and the first semiconductor optical layer 1120 comprising GaPare sequentially formed on the intermediate layer 11. The nucleationlayer 110 and the first semiconductor optical layer 1120 are formedunder different temperature. That is, the nucleation layer 110 is grownin a lower temperature while the first semiconductor optical layer 1120is grown in a higher temperature. To be more specific, the nucleationlayer 110 is formed at a temperature between 300˜550° C. and the firstsemiconductor optical layer 1120 is grown at a higher temperaturebetween 600˜800° C. The thickness of the first semiconductor opticallayer 1120 is larger than that of the nucleation layer 110. In thisembodiment, due to different growing temperature and thickness, thedefect density of the first semiconductor optical layer 1120 is lessthan that of the nucleation layer 110 but larger than that of theintermediate layer 11. In another embodiment, the defect density of thefirst semiconductor optical layer 1120 is larger than or equal to thatof the nucleation layer 110. In another embodiment, the defect densityof the first semiconductor optical layer 1120 is less than or equal tothat of the intermediate layer 11. The growing temperature affects thecomposition of the nucleation layer 110 and the first semiconductoroptical layer 1120. Wherein the nucleation layer 110 comprises morepolycrystalline or amorphous structure and less mono-crystallinestructure than the first semiconductor optical layer 1120 comprises. Inthis embodiment, the first semiconductor optical layer 1120 comprises ahigher defect density than that of the second semiconductor opticallayer 1122. Besides, the energy bandgap of the nucleation layer 110 isbetween that of the intermediate layer 11 and that of the light-emittingstack 12. Wherein the bandgap of the nucleation layer 110 whichcomprises GaP is 2.3 eV, that of the intermediate layer 11 whichcomprises GaN is 3.4 eV, and that of the light-emitting stack 12 whichcomprises AlGaN is 2.1 eV.

Referring to FIG. 9C, the first semiconductor optical layer 1120 isbonded to the second semiconductor optical layer 1122 without adhesivelayer. In this embodiment, a bonded surface is formed between the firstsemiconductor optical layer 1120 and the second semiconductor opticallayer 1122. A surface treatment is performed on the first semiconductoroptical layer 1120 and the second semiconductor optical layer 1122 tosmooth the surfaces before connecting the structure in FIG. 9A and FIG.9B. Wherein the surfaces are attached to each other and the surfacetreatment is applied to enhance the bonding strength between thesurfaces. Moreover, the surface treatment also removes impurities on thesurfaces and reduces the amount of light being absorbed by theimpurities. In another embodiment, the bonded surface is almostdiminished after surface treatment applies. The surface treatment can befast atom bombardment (FAB) or plasma surface treatment. To be morespecific, the FAB uses argon as an atom source providing atoms forbombarding the surface and the plasma surface treatment uses oxygen as aplasma source providing plasma hitting the surfaces. After surfacetreatment, the process of connecting the two structures is performedunder a specific vacuum level wherein the reaction chamber for theprocess has a pressure less than 10⁻⁵ Pa. To be more specific, theprocess is performed at a vacuum level wherein the pressure of thereaction chamber is between 10⁻⁶˜10⁻⁸ Pa.

After connecting the first semiconductor optical layer 1120 and thesecond semiconductor optical layer 1122, the growth substrate 90 isremoved, Referring to FIG. 9D, portions of the n-type semiconductorlayer 123, the active layer 122, the p-type semiconductor layer 121, thesecond semiconductor optical layer 1122, and the second window layer 140are removed to expose the first window layer 112. To be more specific,portions of the first window layer 112 are removed to form a recessportion 131 and a flat surface 132 is defined between the light-emittingstack 12 and the second semiconductor optical layer 1122.

Referring to FIG. 9E, a plurality of contacts 171 are formed on thesecond window layer 140. Then, the insulation layer 181 is formed tocover side walls of the light-emitting stack 12, side walls of the firstwindow layer 112, the recess portion 131 of the first window layer 112,and the second window layer 140, but not to cover the contacts 171.

Referring to FIG. 9F, portions of the insulation layer 181 formed on therecess portion 131 of the first window layer 112 are removed to exposeparts of the first window layer 112. Then, the first electrode 16 isformed on the exposed first window layer 112, and an extension part 172is formed on the contacts 171 to form the second electrode 170.

Referring to FIG. 9G, a reflective layer 101 to increase the laterallight extraction is formed on a surface of the permanent substrate 10opposite to the light-emitting stack 12. Then, a carrier 103 is formedon the reflective layer through an adhesive layer 102. The reflectivelayer 101 and the adhesive layer 102 have widths substantially the sameas the width of the permanent substrate 10. The carrier 103 has a widthwider than that of the reflective layer 101 or that of the first windowlayer 112.

It will be apparent to those having ordinary skill in the art thatvarious modifications and variations can be made to the devices inaccordance with the present disclosure without departing from the scopeor spirit of the disclosure. In view of the foregoing, it is intendedthat the present disclosure covers modifications and variations of thisdisclosure provided they fall within the scope of the following claimsand their equivalents.

What is claimed is:
 1. A light-emitting device, comprising: a substrate;an intermediate layer on the substrate; a first window layer comprisinga first semiconductor optical layer on the intermediate layer and asecond semiconductor optical layer on the first semiconductor opticallayer; and a light-emitting stack on the second semiconductor opticallayer; wherein a difference between the lattice constant of theintermediate layer and the lattice constant of the first semiconductoroptical layer is greater than 2.3 Å.
 2. The light-emitting device ofclaim 1, wherein the first semiconductor optical layer comprises ahigher defect density than that of the second semiconductor opticallayer.
 3. The light-emitting device of claim 1, wherein the intermediatelayer and the first semiconductor optical layer comprise different groupIII-V semiconductor compounds and the substrate comprises anon-semiconductor material.
 4. The light-emitting device of claim 1,further comprising a nucleation layer between the intermediate layer andthe first window layer.
 5. The light-emitting device of claim 4, whereinthe first semiconductor optical layer comprises a phosphidesemiconductor compound.
 6. The light-emitting device of claim 4, whereinthe intermediate layer comprises a nitride semiconductor compound andthe nucleation layer comprises a phosphide semiconductor compound. 7.The light-emitting device of claim 4, further comprising: a secondwindow layer on a side of the light-emitting stack opposite to the firstwindow layer; and a passivation layer on the first window layer and thesecond window layer.
 8. The light-emitting device of claim 7, furthercomprising a first electrode on the second window layer not covered bythe passivation layer and a second electrode on the first window layernot covered by the passivation layer.
 9. The light-emitting device ofclaim 7, wherein the passivation layer has a refractive index smallerthan the refractive index of the second window layer.
 10. Thelight-emitting device of claim 9, wherein the intermediate layer has arefractive index between the refractive index of the substrate and therefractive index of the nucleation layer or the first window layer. 11.The light-emitting device of claim 4, wherein an energy bandgap of thenucleation layer is between that of the intermediate layer and that ofthe light-emitting stack.
 12. The light-emitting device of claim 4,wherein the nucleation layer is lattice matched with the first windowlayer and lattice mismatched with the intermediate layer.
 13. Thelight-emitting device of claim 12, wherein the substrate is latticemismatched with the intermediate layer.
 14. The light-emitting device ofclaim 5, wherein the nucleation layer has a thickness less than athickness of the first semiconductor optical layer.
 15. Thelight-emitting device of claim 1, wherein the first semiconductoroptical layer and the second semiconductor optical layer comprise thesame material.
 16. The light-emitting device of claim 1, furthercomprising a bonded interface between the first semiconductor opticallayer and the second semiconductor optical layer.
 17. The light-emittingdevice of claim 1, further comprising a reflective layer formed on asurface of the substrate opposite to the light-emitting stack.
 18. Thelight-emitting device of claim 1, wherein the nucleation layer comprisesgallium phosphide (GaP).
 19. The light-emitting device of claim 18,wherein the intermediate layer comprises gallium nitride (GaN).
 20. Thelight-emitting device of claim 1, wherein the intermediate layercomprises gallium nitride (GaN).